Arrangement and Methods for Increasing Productivity of a Tissue Papermaking Machine or Minimizing its Dimensions

ABSTRACT

A papermaking machine is provided for manufacturing a paper web, comprising a forming section having two clothings, a dewatering section comprising at least one paper manufacturing clothing, and a plurality of rotary rolls comprising guide rolls, each guide roll having two opposing flanges interconnected by a shell, each clothing running about some of the rotary rolls in a loop, wherein said papermaking machine is a tissue papermaking machine, at least one of the guide rolls is a lightweight guide roll supporting at least one of the clothings, and at least one of the shell and the flanges of said lightweight guide roll comprises a material with a density less than steel, wherein a weight of the lightweight guide roll is at least 10% less than a weight of a steel guide roll having the same dimensions and mechanical parameters. Associated devices and methods are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. §371 national phase entry of PCT/SE2006/001299, filed Nov. 16, 2006, which claims priority to Swedish Application No. 0502801-4, filed Dec. 19, 2005, all of which are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an arrangement and methods for increasing productivity of a tissue papermaking machine by increasing the operation speed, minimising vibrations and/or decreasing the machine dimensions in a cost efficient way with unchanged productivity.

2. Description of Related Art

The machine productivity, the amount of paper that could be produced during a given time, depends on a number of factors such as a width of the machine and its processing speed. The increasing of the machine width could create a number of technical problems depending on the increasing weights of all machine elements, particularly, rotating elements such as rolls mounted on a machine frame. Such elements, due to rotating of high masses at a high speed cause vibrations, and, as a consequence, these vibrations limit the increase of the operation speed and the production of the entire machine. The problem is described in PCT/FI2005/050092 publication and solved by a special roll construction.

The conventional papermaking machine comprises a large amount of different rotating elements such as different rolls supporting paper webs of different grades and qualities and board webs and/or the paper machine clothing used for paper manufacturing purpose in the different paper machine sections. The different rolls have different functions and different placements in the machine sections as will be described below.

Guide or leading rolls are used for support of the paper web or the machine clothing or used for changing the direction of movement of the web, the wire, the fabric or the felt. The guide rolls support a number of fabrics used for paper web manufacturing in a forming section, in a dewatering section, a drying section and, alternatively in a winding section. Tension rolls are the guide rolls that automatically regulate the tension of the wire or the other kind of papermaking clothing.

Stretching rolls are used as the adjustable guide rolls, which stretch the felt or the wire so that the tension roll can achieve its purpose. Spreader rolls smooth out the moving wire, felt, fabric or the web in the lateral direction and thus prevent the development of longitudinal folds. Alignment rolls are adjustable guide rolls for guiding the wire or the felt. A forming roll or a breast roll is a guide roll supporting the wire in the forming section of a fourdinier, a twin wire or another former types, and changes the direction of movement of the wire immediately prior to the forming zone.

All conventional rolls as described above have different functions and with a very few exceptions, like suction press rolls, usually comprise two flanges having shafts for mounting of the roll on a machine frame via a bearing house or other suitable means and a shell connecting those flanges in one piece of equipment. The shell could be connected to the flanges in many different ways that are not to be discussed here. The shell thickness could widely vary, and usually the roll is hollow inside in order to decrease its weight. All conventional rolls as mentioned above are made of metal, usually of steel. The nowadays tissue papermaking machines can be run at about 800-1200 m/min up to maximum about 2200 m/min. For given machine frame dimensions the further increase of the machine speed is limited by vibrations created due to rotation of the big amount of different heavy steel rolls that are mounted on the machine frame for, among others, supporting the different fabrics used in paper manufacturing. Such arrangement will be very expensive.

For instance, the conventional steel guide roll can weigh from 900 up to 10 000 kilogram depending on its length, that could be between 1 and 9 m, and the diameter between 300 and 1200 mm.

These vibrations caused by the rotation of those rolls are spread through the machine frame and could be transferred also through the fabrics. The critical vibration, when the rolls achieve their critical frequency, which can lead to destroying of the rotating rolls and other equipment, do not allow further machine speed and productivity increasing. Usually the steel rolls are not machined from their inner side as it is very costly and thus only allowed to be run up to ½ of its own critical speed without causing troubles. The steel rolls always have a residual unbalance, which in its turn creates vibrations of the frame, on which the rolls are to be mounted.

Thus, it is known in the art that the process speed of the existing papermaking machines cannot be increased due to the vibrations and bending parameters of the rotating rolls such as, among others, the guiding rolls for the clothing.

An attempt to decrease the weight of the steel guide rolls by reducing their diameters may decrease their critical rotation speed and increase the undesired bending. The nowadays steel guide rolls, for instance in drying section, are running nearly at a half of the critical speed, and therefore they could cause the vibrations. Even the residual unbalance of the rolls may cause undesired vibrations.

The vibrations, as was mentioned above, occur in the different sections of the paper machine due to rotating of the different elements such as dry cylinders, guide rolls, leading rolls, a forming roll and the like. The vibrations could be transferred through the entire machine via a frame, on which the rotating elements are mounted, and through the clothing running about the rotating elements in the loop or through the machine foundation.

The rotating elements are made of metal material, often of steel and are heavy. These rotating heavy elements always have a residual unbalance when mounted on a carrying construction or the frame and therefore, when rotated at high speed, they create forces having the corresponding frequencies and therefore also vibrations. These forces could be calculated according to the formula (1):

F=1/2S×M×(2πf), wherein:   (1)

-   F—created force, -   M—rotating mass -   S—total unbalance depending on the roll own unbalance and its     mounting -   f—frequency of rotation

The traditional solution of the problem with bending of the roll is to increase the diameter of the steel roll for achieving a higher stiffness and a higher critical speed. Sometimes it is also possible to increase the shell wall thickness in order to achieve higher stiffness and therefore, also less deflection. This leads to increasing of the roll weight, higher inertia and corresponding unbalance forces, and requests a machine carrying frame modification that is not always desirable, as heavier rolls request more massive frame for supporting them. The frame modifications are not always desired also due to a down time and a loss of the production, rather costly due to material costs.

Alternatively, when the machine speed and productivity are satisfactory, one could desire to reduce the machine dimensions for new installations or re-builds that is limited by the problems with own frequencies of the rotating rolls, their bending parameters and caused vibrations as described above.

SUMMARY OF THE INVENTION

The present invention provides a solution to the problems associated with the own frequencies of the rotating rolls, the vibration caused by their rotation at high speed as mentioned above and allows substantially increase of the operation speed. Alternatively, the invention allows decreasing the machine dimensions for a given process speed comparing to the conventional solutions in a cost efficient way.

Therefore, the best way to reduce the undesired excitation forces, as illustrated above in formula (1) is a reduction of the rotating mass, for instance by using a lightweight material. Stainless steel has a density of about 7800 kg/m³, titanium is about 4500 kg/m³, aluminium is about 2700 kg/m³, while the composite materials, like carbon or glass fiber reinforced resin or other polymer, have density between 1500 and 2000 kg/m³.

The roll made of the composite material with the same diameter as the steel roll will weigh only about 20-30% of the steel roll weight. Thus, an essential reduction of the weight of the roll will lead to the essential reduction of the excitation forces and vibrations that this roll will cause due to its rotation.

Thus, the present invention is directed to use of lightweight rolls for guiding and/or supporting wires, fabrics or other clothing in a tissue papermaking machine. The lightweight rolls made of lighter materials with the required bending and rigidity parameters could be of the smaller, the same or even larger diameter than the conventional metal rolls, usually made of steel. The lightweight roll of composite material with larger diameter may weigh less than the corresponding steel roll with larger diameter, and therefore it might be possible to use even larger composite rolls and still achieve a reduction of the excitation forces. The lighter weight of the rolls allows increasing of the rotating speed of the rolls without increasing the corresponding critical vibrations of the rolls and as a result, increasing the speed of the operation. The roll according to the invention may have one of the shell and the flanges made of the lightweight material or the both parts thereof. Alternatively, the entire roll could be made as one piece from the lightweight material by conventional methods as moulding, powder pressing or the like.

This invention allows increasing of the operation speed of the tissue papermaking machine and, thus, increasing the total productivity for a new machine for the chosen machine width and footprint.

The invention concerns also a re-build of an existing tissue papermaking machine for increasing the production speed due to usage of the lightweight rolls in the existing space. The lightweight rolls for higher speeds made of the composite materials do not require the roll diameter increase and the machine frame modifications, as they can be dimensioned to the same diameter as the original conventional steel rolls.

An object of the invention is to decrease the tissue papermaking machine vibrations due to decreasing the weight of the rolls.

Still another object of the invention is increasing a possible machine frame production by increasing the possible rotating speed of the rolls supporting the clothing.

Still another object of the invention is reducing the machine dimensions for a given operation speed comparing to the conventional solutions with unchanged productivity due to minimized machine frame vibrations caused by the rotating rolls.

Another object of the invention is increasing of the speed of production, for instance, when the machine is to be re-built without increasing the dimensions of the machine or with a new machine with the limited space and the footprint.

The invention refers to a papermaking machine for manufacturing a paper web, the papermaking machine comprising at least a forming section having two clothings, a dewatering section comprising at least one paper manufacturing clothing, and a plurality of rotary rolls, each of said rotary rolls having two opposing flanges and a shell interconnecting the flanges, the rotary rolls being configured to support the clothings, each clothing running about some of the rotary rolls in a loop, said rolls each having a diameter and being dimensioned for mechanical parameters including calculated load, bending parameter and rotating speed, wherein said papermaking machine is a tissue papermaking machine,

at least one of the rolls is a lightweight roll supporting at least one of the clothings of the tissue papermaking machine, and

at least one of the shell and the flanges of said lightweight roll comprising a material with a density less than steel, wherein a weight of the lightweight roll is at least 10% less than a weight of a similar roll comprised of steel and having the same dimensions and the same mechanical parameters.

The lower density of the alternative material provides rolls with decreased weight per length unit for the same roll dimensions. The weight of the lightweight roll should be at least 10% less comparing to the weight of the corresponding steel roll having approximately the same dimensions and the same mechanical parameters. At least one roll, or preferably at least 10% of all rolls in at least one of the machine sections should be exchanged from the steel rolls to the rolls according to the invention in order to achieve a visible effect on vibration level in the machine and allow higher operation speed.

The invention also refers to a method of increasing an operation speed of a tissue papermaking machine, the tissue papermaking machine comprising at least a forming section having two clothings, a dewatering section comprising at least one paper web supporting clothing, and a plurality of rotary rolls, each of said rotary rolls having two opposing flanges, each with a mounting shaft, and a shell interconnecting the flanges, the rotary rolls being configured to support the clothings, each clothing running about some of the rotary rolls in a loop, said method comprising:

substituting at least one of the shell and the flanges of a steel roll with a corresponding at least one of a shell and flanges comprised of a material having a lower density than steel and the same mechanical properties as steel.

The invention also refers to a method of using a lightweight roll in a tissue papermaking machine, the lightweight roll comprising two opposing flanges and a shell interconnecting the flanges, wherein at least one of the shell and the flanges is comprised of a material with a density less than steel, wherein a weight of the lightweight roll is at least 10% less than a weight of a similar roll comprised of steel and having the same dimensions and the same mechanical parameters, each roll having a diameter and being dimensioned for mechanical parameters including calculated load, bending parameter and rotating speed, said method comprising:

substituting at least one steel rotary roll with a lightweight roll having a weight of between about 10% and about 90% of and the same bending parameter as the steel rotary roll, each roll being configured for at least one of guiding and supporting at least one of a wire, a fabric, and a clothing in at least one of the sections of the tissue papermaking machine.

The invention also refers to a method of minimizing dimensions of a tissue papermaking machine having a given operation speed, comprising:

substituting at least one steel rotary roll in at least one section of the tissue papermaking machine with a lightweight rotary roll having at least one of a shell and opposing flanges comprised of a material having a lower density than steel and the same mechanical parameters as steel.

The invention also refers to a method of decreasing vibrations while increasing an operation speed of a tissue papermaking machine, the tissue papermaking machine comprising at least one of a forming section, a dewatering section, a drying section and a winding section, each section comprising at least one paper web supporting clothing and a plurality of rotary rolls, each of said rotary rolls having two opposing flanges and a shell interconnecting the flanges, the rotary rolls being configured to support the clothings, each clothing running about some of the rotary rolls in a loop, said method comprising:

substituting at least one of the shell and the flanges of a steel rotary roll by the corresponding at least one of a shell and the flanges comprised of a material having a lower density than steel and the same mechanical properties as steel.

The invention also refers to a method of re-building a tissue papermaking machine with a given dimension and a required operation speed, the tissue papermaking machine comprising at least one of a forming section, a dewatering section, a drying section and a winding section, each section comprising at least one paper web supporting clothing and a plurality of rotary rolls, each of said rotary rolls having two flanges and a shell interconnecting the flanges, the rotary rolls being configured to support the clothings, each clothing running about the rotary rolls in a loop, said method comprising:

substituting at least one of the shell and the flanges of a steel rotary roll with a corresponding at least one of a shell and flanges made of a material having a lower density than and the same mechanical properties as steel.

The usage of the lightweight rolls, which are fitting in the existing space due to their smaller diameters comparing to the corresponding steel rolls, allows conducting a re-build and speeding up of the existing tissue papermaking machines.

It is to be understood that the term “guide roll” or “leading roll” is used in this context not as a limiting only to the guide or leading rolls and should be interpreted as referring to the all different types of rolls or rotating elements supporting different clothing in the papermaking machine which were described above.

Thus, the inventive idea is to make the rotating elements as rolls, carrying and supporting wires, fabrics and other clothing or paper and board webs, of the reduced weight comparing to the corresponding conventional steel roll with the same dimensions and mechanical parameters in such a manner that these rolls create less vibrations in the machine and allow sufficiently increase of the speed of the roll rotation and the speed of run of the supported clothing, and as a consequence, the productivity of the entire machine.

The invention will now be described in more detail with reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a layout of a tissue machine with a C-former, a wet end, a dewatering section and a Yankee dryer. The three clothings of the machine, including two forming wires and a dewatering fabric, are supported by the guide rolls according to the invention.

FIG. 2 shows a layout of a tissue machine with a Crescent former and two clothings and a Yankee dryer. The clothings, including the forming wire and the dewatering fabric, are supported by the guide rolls according to the invention.

FIG. 3 shows a layout of a tissue machine with a Crescent former, a Yankee dryer and a winding section comprising the clothing supported by the guide rolls according to the invention.

FIG. 4 shows an alternative drying section comprising a Yankee dryer followed by a can dryer. In the drying section employing the drying cylinders or the cans, the drying fabric runs about the guide rolls according to the invention.

FIG. 5 is a cross section of a roll according to the invention. The roll has two flanges and a shell.

FIG. 6A shows a cross sectional enlarged view of the conventional steel roll shell and

FIG. 6B shows a composite roll shell.

FIG. 7 is a diagram showing differences in vibrations levels, [total RMS 2-1000 HZ] caused by a steel leading roll or a composite leading roll in the same position in a papermaking machine. The vibrations are measured in machine direction on a bearing house of the leading roll at different machine speeds from 1200 m/min to 1600 m/min.

FIG. 8 is a diagram showing vibrations levels [peak values] caused by steel leading roll and composite leading roll in the same position in a papermaking machine at rotational and double rotational frequencies for the corresponding rolls. The diagram shows the peak vibration levels at the rotational frequency and the double rotational frequency for the roll in leading roll position for the conventional steel roll (two lines above) and the lightweight roll (two lines below) according to the invention. The vibrations are measured in machine direction on the bearing house of the leading roll and at the same roll position in the machine.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 a layout of a machine for manufacturing a tissue paper web is illustrated. The machine has a wet end 1, wherein a paper web 11 is formed in a C-former. A headbox 12 delivering a paper stock between an outer forming wire 13 supported by a plurality of guide rolls 10 and an inner forming wire 14 also supported by a plurality of guide rolls 10. The wires 13, 14 run over a guide roll denoted forming or breast roll 8. The paper web 11 is formed on the inner forming wire 14. The web 11 is partly dewatered while being between the wires 13, 14 and then the paper web 11 is further transferred by a pick-up device 9 from the outer forming wire 14 to a carrying fabric 19 of a dewatering section 2. The pick-up device 9 may be any one known in the art. The web 11 is further dewatered in the dewatering section 2 by, for instance, known in the art vacuum suction devices of different types such as a suction box or a vacuum roll, in order to increase dry content of the web 11. The carrying fabric 19 could be a press fabric or other type of the suitable machine clothing. The dewatering section 2 is followed by a drying section 3. The drying section 3 comprises a drying cylinder 5, a so called Yankee dryer 5. When the paper web 11 is dewatered to approximately 25-60% of dry content, it is further transferred or pressed against a drying surface of the Yankee dryer 5 by a transfer roll 6 for a final drying. To insure the web 11 transfer to the Yankee dryer 5 drying surface, the different types of adhesive application devices might be employed (not shown). The web 11 could be only transferred to the Yankee dryer for a contact drying without any sufficient compression of the web 11 or, alternatively, the paper web 11 could be pressed against the Yankee dryer 5 by a press device, comprising the Yankee cylinder 5 and a press roll 6 or 7, for instance. The alternative additional press arrangement in the dewatering section 2 is not shown while it could be also used for pre-pressing or structuring of the web 11. The carrying fabric 19 used as a dewatering or a press fabric and carrying the web to the drying section 3 runs about a plurality of the rotary guide rolls 10 in form of stretch rolls. A roll 6 is used as a transfer roll, and a roll 7 is used for increasing the paper web dryness, when transferred to a Yankee dryer 5 for the final drying of the paper web 11 in the drying section 3.

Alternatively, the carrying fabric 19, instead of being the dewatering or press fabric, could be a through-air-drying fabric in another embodiment of the invention, wherein the tissue paper web is to be dried by a so called through-air drying (TAD) technology on a TAD-cylinder without using the conventional Yankee dryer.

In the embodiment shown in FIG. 1, at least a part of the guide rolls 10 supporting the carrying fabric 19 in the dewatering section 2 are lightweight guide rolls 10 according to the invention made of the composite material, which are inserted instead of the conventional steel guide rolls. As the weights of rotary guide rolls 10 have been decreased, the machine fabric could be run at higher speeds that, in its turn, influences the machine productivity. In order to achieve a sufficient result in decreasing the vibrations caused in the machine by the rotating of heavy steel guide rolls, at least one, or preferably at least 10% of all guide rolls should be inserted by the lightweight guide rolls. The more visible effect could be achieved when more than 50% of the rotary steel guide rolls are inserted by the corresponding lightweight guide rolls 10.

The lightweight guide roll 10 according to the invention should have the weight at least 10% less than the corresponding steel guide roll with the same mechanical properties, preferably the lightweight roll weight should be reduced by at least 20-30% of the corresponding steel guide roll weight, and most preferably by 60-80% of the corresponding steel guide roll weight remaining the required mechanical properties as of the corresponding steel rolls. The decrease of the roll weight is achieved by use of alternative materials having a density lower than the steel density. For example, such materials could be lightweight metal such as titan, aluminium and the like. The other alternative is composite materials comprising a glass or carbon reinforcing fibre and a resin matrix. Alternatively, other suitable materials such as ceramic and the like with the lower density and suitable mechanical properties could be used for manufacturing such lightweight guide rolls.

Alternatively, the conventional steel guide or leading rolls in the wet end 1 could be replaced by the lightweight guide rolls 10 as described above in the loops of the inner, the outer or both of the forming wires 13, 14.

FIG. 2 shows a modified tissue paper machine layout with a Crescent-former in the wet end 1. The wet end 1 comprises an outer forming wire 13 and a fabric 19. Each of the forming wire 13 and the fabric 19 run about a plurality of guide and/or stretch rolls 10, at least one of said guide rolls 10 is substituted by the lightweight guide roll according to the invention. The fabric 19 carries the formed paper web 11 through the dewatering section 2 from the wet end 1 to the drying section 3 for the final drying on the Yankee dryer 5. The dewatering section 2 could alternatively comprise also a press device (not shown).

FIG. 3 illustrates a further modified tissue paper machine layout with a Crescent-former having the wet end 1, the dewatering section 2 and the drying section 3. The drying section 3 is followed by a winding section 4, wherein the finally dried paper web 11 is creped from the Yankee dryer 5 drying surface by a doctor and further transported from the Yankee dryer 5 to a reel-up device for winding the paper web 11 into a paper roll 18. The tissue paper web 11 is supported by a support clothing 21 that runs about a plurality of the guide rolls 10. Alternatively, the web 11 could be calendered by a calender (not shown) prior to winding into the roll 18. The clothing 21 could be any suitable fabric, including a TAD-fabric, if a TAD-unit is used after the Yankee dryer for the final drying of the tissue web 11. The reel-up device could be of any known type and will not be discussed closer here.

The guide rolls 10 are lightweight guide rolls according to the invention and made of the lightweight material or a composite material. At least some of them do not have a special drive (not shown) for rotation and being driven by the moving fabric 19. The composite material of the guide rolls 10 is preferably made of a carbon fibre reinforced resin, but other compounds could be used instead of resin as well as other kind of reinforcing fibers. The lightweight or composite guide rolls 10 alternatively could be made by the conventional casting- or moulding methods known in the art.

Alternatively, the conventional steel guide- or leading rolls in the winding section 4 could also be replaced by the lightweight guide rolls 10.

FIG. 4 illustrates still another embodiment of the papermaking machine having a modified drying section 3. In the drying section 3, the drying cylinder 5 (so called Yankee dryer 5) is followed by a number of drying cylinders 20 or cans for the final drying of the paper web 11. Alternatively, the drying section 3 could exclude the Yankee dryer 5 and comprise only the drying cylinders 20 for drying the paper or board webs. The web 11 is supported by a support or drying fabric 22 that presses the web 11 towards the drying cylinder 20 drying surface. The fabric 22 runs about a plurality of the lightweight guide rolls 10 according to the invention. After being finally dried, the web 11 is wound into the paper roll 18 in the winding section 4 of the known type.

Alternatively, the conventional steel guide or leading rolls in the drying section 3 could be replaced by the lightweight guide rolls 10 according to the invention.

In FIG. 5, a sectional view of a lightweight guide roll according to the invention is illustrated. The roll 10 has two flanges 15 with shafts 16 adopted to be rotary mounted into a bearing house or in any other suitable manner. The roll 10 has also a roll shell 17 interconnecting these flanges 15 into one piece of the equipment. The roll shell 17 is adopted to support the paper web 11 or different clothing used into the papermaking machine. The roll shell 17 can be mounted to the flanges in any suitable known way. One of the flanges 15 and/or roll shell 17 might be made of the material having density less than steel in order to reduce the total weight of the roll 10 for about 10-90%.

Alternatively, the roll 10 might be made from the known alternative lower density lightweight materials, such as composites and/or plastics, as a whole by the suitable known manufacturing methods like moulding, extruding or the like, and therefore will have the shell 17 being integrated with the flanges 15 in one piece.

The roll 10 according to the invention is a hollow roll, but when manufactured from the lower density lightweight materials, such as, for instance, composite material or plastics, the roll 10 might have a solid design.

FIG. 6A illustrates a cross sectional view of the guide roll having the conventional steel shell 17 and FIG. 6B—a composite shell 17 for the corresponding lightweight roll 10 made of composite material, partly or entirely. When the shell 17 of the roll 10 made of the composite material having the lower density than steel, the shell 17 might have alternatively the same or different thickness and outer diameter compared to the corresponding conventional heavier steel roll shell with the same mechanical properties. These mechanical properties depend on the calculated required mechanical parameters required for the stabile roll 10 performance in the particular place into the papermaking machine. The required parameters for the lightweight roll 10, substituting the steel roll, such as bending, stiffness, critical speed, inertia, possible maximum rotation speed, vibration, residual unbalance and the required dimensions could be calculated by the known methods.

As an alternative to the composite material, the rolls 10 can be made, partly or entirely, of light ceramics by the precise pressing or other conventionally known technologies.

Furthermore, the lightweight metals like titanium and aluminium could also be used for the manufacturing of the lightweight guide rolls for papermaking machine. These methods preferably should be of kind precise casting and preferably avoiding the additional working of the roll surfaces. The lightweight guide roll 10 may have a special cover layer on its surface for achieving particular surface qualities.

The composite rolls according to the invention, due to its good weight-to-stiffness ratio have a very small deflection and high nominal frequencies of vibration; they can have weight of 10-20% of the corresponding steel roll and could have smaller diameter for the same application. Those rolls are easy to handle, to transport and store. They ideally suit for the limited space application for re-build and/or speed-up projects and costs reduction. On the other hand, it is clear that the roll shell made of other than metal material has another requirements in regard to assembling of the composite shell to the metal roll shafts, but this constructive difference will not be discussed here.

It has been noted, for instance, that decreasing of the guide roll weight allows sufficiently increase of the rotating speed of the roll before it reaches the critical speed, and lighter rotary elements create less vibrations due to their lower residual unbalance forces. The composite rolls do not have ½ critical speed limitation, as the manufacturing methods allow achieving a perfect circular cross section of the roll shell. So, the composite rolls have higher critical speed and allow run to almost 1/1 critical speed.

Thus, using another materials than steel having a lower density and consequently lighter weight, the weight of the rotary rolls could be decreased up to 80-10% of the weight of the corresponding steel rolls of the same diameter. It has been tested and approved that the lightweight roll with about 20% weight of the conventional steel roll of the same diameter could increase the rotation speed up to the double critical speed comparing to the conventional steel roll without reaching the own critical speed, see the formula (2) below, and do not create the corresponding undesired vibrations due to higher residual unbalance forces as illustrated by FIG. 7 and FIG. 8.

n_(critical composite)≈2×n_(critical steel),   (2)

wherein n is a critical rotation speed.

The machine frame modifications are not required in the case, when the higher rotation speed is required and achieved by the lightweight rolls, that saves investment costs. The roll change is easier to conduct due to lighter weight of the rolls, therefore the down time for their mounting is shortened also.

For example, the reference steel roll having a diameter of 650 mm has a weight of about 4 000 kg, while the roll made of the composite material with same diameter of 650 mm has a weight of only 800 kg.

It is known in the art that the lighter the rotating element, the lower will be the corresponding excitation forces for the element having the same stiffness; the higher the critical speed of the rotating element, when the undesired vibrations occur, the higher speed of rotation is possible for the element and thus, a higher process speed for the entire machine could be achieved. Therefore, with the lighter rotating elements such as the guiding, stretching or leading rolls carrying and supporting the clothing or the paper web, for instance, the machine speed could be increased up to 3000 m/min or more. Alternatively, remaining the same operation speed it will be possible to reduce the machine dimensions if desired.

Due to its lighter weight, the composite roll has a low moment of inertia and as a consequence, a lower power consumption that also saves costs. This saves investment and maintenance costs. The material for manufacturing the lightweight rolls could be chosen from the different composite materials, such as among others a fibre reinforced composite or resin, and/or ceramics. These materials are very resistant to the most of chemicals. These rolls could be moulded very accurately and do not require after working, machining or finishing. They could have a very exact round shape of the composite shell and excellent dimensional stability achieved by the optimal filament winding angles during manufacturing that minimises the vibrations as well. A coefficient of a thermal expansion for the carbon fibre tube shell, for instance, is about 10 times less than with the corresponding steel roll in the axial direction. The lightweight composite materials, such as carbon or glass fibre with a polymer resin matrix, have good vibrations damping properties and high balancing accuracy. As a consequence, the rolls made of such materials have low residual unbalance and low level of vibrations over the whole operating speed range. The lightweight rolls could additionally have a covering layer for achieving special surface properties.

In FIG. 7 vibrations caused by a steel leading roll is compared with vibrations caused by a composite leading roll used as a leading roll in the same position in a papermaking machine. The steel roll and the composite roll were measured at different machine speeds. The measured results are illustrated as in the diagram. One can see that the corresponding composite rolls have the vibration level sufficiently lower at the different rotational frequencies than the corresponding steel rolls.

It can clearly be seen that the steel roll in the position as a leading roll causes more than double vibration level which increases with increasing of the machine operating speed.

The lightweight guide rolls could be used in all sections of the papermaking machine: in the forming section of the paper machine as guide or leading rolls, in a drying section 3 as measuring tension rolls for control of the clothing tension or as alignment rolls for felts, fabrics or wires. The lightweight rolls could be used as spreading rolls, forming or breast rolls. Drying cylinders or the like may be manufactured of lightweight metal.

The paper machine in question could be a conventional paper, board or tissue manufacturing machine.

It is to be understood that the invention is not limited to the embodiments of the papermaking machines shown and should be interpreted in the spirit of the invention. The invention is applicable to the other types of the non-conventional paper manufacturing machines such as, for instance, so called through-air-drying (TAD) machines. 

1. A papermaking machine for manufacturing a paper web, the papermaking machine comprising at least a forming section having two clothings, a dewatering section comprising at least one paper web supporting clothing, and a plurality of rotary rolls, each of said rotary rolls having two opposing flanges and a shell interconnecting the flanges, the rotary rolls being configured to support the clothings, each clothing running about some of the rotary rolls in a loop, said rolls each having a diameter and being dimensioned for mechanical parameters including required calculated load, bending parameter and rotating speed, wherein said papermaking machine is a tissue papermaking machine, at least one of the rolls is a lightweight roll supporting at least one of the clothings of the tissue papermaking machine, and at least one of the shell and the flanges of said lightweight roll comprising a material with a density less than steel, wherein a weight of the lightweight roll is at least 10% less than a weight of a similar roll comprised of steel and having the same dimensions and the same mechanical parameters.
 2. The tissue papermaking machine of claim 1, wherein the weight of the lightweight roll is reduced by at least between about 20% and about 30%, and most preferably by between about 60% and about 80%, as compared to the weight of the similar roll comprised of steel.
 3. The tissue papermaking machine of claim 1, wherein the lightweight roll has a diameter smaller than a diameter of the similar roll comprised of steel and having the same mechanical parameters.
 4. The tissue papermaking machine of claim 1, wherein the lightweight roll has a diameter larger than a diameter of the similar roll comprised of steel and having the same mechanical parameters.
 5. The tissue papermaking machine of claim 1, wherein the lightweight roll has a diameter equal to a diameter of the similar roll comprised of steel and is configured to rotate at a speed higher than a rotating speed of the similar roll comprised of steel.
 6. The tissue papermaking machine of claim 1, wherein the material of at least one of the shell and the flanges of at least one lightweight roll in at least one of the forming section and the dewatering section of the tissue machine has a density below about 7800 kg/m³, and preferably between about 500 kg/m³ and about 2000 kg/m³.
 7. The tissue papermaking machine of claim 1, wherein at least one lightweight roll is at least partially comprised of the material having a density less than steel, and has the same mechanical parameters, with respect to required calculated load and bending parameter, as the similar roll comprised of steel.
 8. The tissue papermaking machine of claim 1, wherein the tissue papermaking machine further comprises a drying section having drying cylinders and a drying fabric forming a loop and running about the cylinders and at least one lightweight roll.
 9. The tissue papermaking machine of claim 5, wherein the tissue papermaking machine further comprises a winding section having a support clothing forming a loop and running about at least one lightweight roll.
 10. The tissue papermaking machine of claim 1, wherein said lightweight rolls comprise at least one of a lightweight alignment roll, a lightweight stretching roll, a lightweight forming roll, a lightweight tension roll and a lightweight spreader roll.
 11. The tissue papermaking machine of claim 9, wherein said lightweight rolls comprise at least 10% of all rolls in one of the forming and dewatering sections.
 12. The tissue papermaking machine of claim 10, wherein at least one lightweight roll is rotatingly driven by one of the paper web and one of the clothings.
 13. The tissue papermaking machine of claim 1, wherein the shell of the lightweight roll has a cover layer of another material.
 14. The tissue papermaking machine of claim 1, wherein at least one of the shell and the flanges of the lightweight roll is comprised of a composite material.
 15. The tissue papermaking machine of claim 14, wherein the composite material of the lightweight roll is one of a carbon fiber and a glass fiber material with resin matrix.
 16. The tissue papermaking machine of claim 14, wherein the composite material of the lightweight roll is a ceramic material.
 17. The tissue papermaking machine of claim 1, at least one of the shell and the flanges of the lightweight roll is comprised of a lightweight metal having a density less than steel, preferably a density of between about 2000 kg/m³ and about 5000 kg/m³.
 18. The papermaking machine of claim 1, wherein the lightweight roll is a solid roll.
 19. A method of increasing an operation speed of a tissue papermaking machine, the tissue papermaking machine comprising at least a forming section having two clothings, a dewatering section comprising at least one paper web supporting clothing, and a plurality of rotary rolls, each of said rotary rolls having two opposing flanges, each with a mounting shaft, and a shell interconnecting the flanges, the rotary rolls being configured to support the clothings, each clothing running about some of the rotary rolls in a loop, said method comprising: substituting at least one of the shell and the flanges of a steel roll with a corresponding at least one of a shell and flanges comprised of a material having a lower density than steel and the same mechanical properties as steel.
 20. The method of claim 19 further comprising: substituting at least 10% of the steel rolls in at least one section of the tissue papermaking machine with rolls at least partially comprised of the material having the lower density than steel and having a weight of between about 10% and about 90% of and the same mechanical parameters as the steel guide roll.
 21. A method of using a lightweight roll in a tissue papermaking machine, the lightweight roll comprising two opposing flanges and a shell interconnecting the flanges, wherein at least one of the shell and the flanges is comprised of a material with a density less than steel, wherein a weight of the lightweight roll is at least 10% less than a weight of a similar roll comprised of steel and having the same dimensions and the same mechanical parameters, each roll having a diameter and being dimensioned for mechanical parameters including calculated load, bending parameter and rotating speed, said method comprising: substituting at least one steel rotary roll with a lightweight roll having a weight of between about 10% and about 90% of and the same bending parameter as the steel rotary roll, each roll being configured for at least one of guiding and supporting at least one of a wire, a fabric, and a clothing in at least one of the sections of the tissue papermaking machine.
 22. A method of minimizing dimensions of a tissue papermaking machine having a given operation speed, comprising: substituting at least one steel rotary roll in at least one section of the tissue papermaking machine with a lightweight rotary roll having at least one of a shell and opposing flanges made comprised of a material having a lower density than steel and the same mechanical parameters as steel.
 23. The method of claim 22 further comprising: at least one of guiding and supporting at least one of a wire, a fabric, and a clothing with the lightweight roll in at least one section of the tissue papermaking machine.
 24. A method of decreasing vibrations while increasing an operation speed of a tissue papermaking machine, the tissue papermaking machine comprising at least one of a forming section, a dewatering section, a drying section and a winding section, each section comprising at least one paper web supporting clothing and a plurality of rotary rolls, each of said rotary rolls having two opposing flanges and a shell interconnecting the flanges, the rotary rolls being configured to support the clothings, each clothing running about some of the rotary rolls in a loop, said method comprising: substituting at least one of the shell and the flanges of a steel rotary roll by the corresponding at least one of a shell and the flanges comprised of a material having a lower density than steel and the same mechanical properties as steel.
 25. A method of re-building a tissue papermaking machine with a given dimension and a required operation speed, the tissue papermaking machine comprising at least one of a forming section, a dewatering section, a drying section and a winding section, each section comprising at least one paper web supporting clothing and a plurality of rotary rolls, each of said rotary rolls having two flanges and a shell interconnecting the flanges, the rotary rolls being configured to support the clothings, each clothing running about the rotary rolls in a loop, said method comprising: substituting at least one of the shell and the flanges of a steel rotary roll with a corresponding at least one of a shell and flanges made of a material having a lower density than and the same mechanical properties as steel. 